Nonwoven webs made from overlapped or entangled filaments or fibers of melt-processable thermoplastic polymers are commonly produced using spunbond and meltblown processes. Nonwoven webs are incorporated into many consumer and industrial products, such as single-use or short-life hygienic products, disposable protective apparel, fluid filtration media, and durables like bedding and carpeting. Nonwoven webs are fashioned by the operation of a meltspinning apparatus in either a spunbond process or a meltblown process.
A spunbond process generally involves extruding a curtain of fine diameter, semi-solid filaments of one or more thermoplastic polymers from multiple rows of fine orifices in a spinneret. A voluminous flow of relatively cool process air is directed at the curtain of extruded filaments to quench the molten thermoplastic polymer. The filaments are attenuated or drawn to a specified diameter and oriented on a molecular scale by drag forces created by a high-velocity flow of process air. The drawn filaments are propelled by the high-velocity air flow in a filament/air mixture toward a forming zone and collected on a moving collector to form a continuous length spunbond nonwoven web.
A meltblown process also involves pumping a thermoplastic polymer from an extruder through a die to form a curtain of filaments. However, converging layers of heated air, typically discharged from slots or holes on opposite sides of the curtain of filaments, contact the filaments immediately after extrusion and, through concomitant drag forces, stretch and attenuate the filaments. The filaments are collected on a moving collector forming a continuous length meltblown nonwoven web. Generally, meltblown filaments are finer than spunbond filaments and meltblown nonwoven webs are more fragile than spunbond nonwoven webs. Nonetheless, spunbond and meltblown nonwoven webs are susceptible to damage arising from mechanical contact, particularly before consolidation by a process such as calendaring. After consolidation, the nonwoven web is wound into a roll and removed from the meltspinning apparatus to another location for forming a consumer or industrial product.
The consolidated nonwoven web may be unwound from the roll and then folded with a fold line extending longitudinally along its continuous length to form a finished product. One type of folding device is a stationary folding board or skid plates that defines a chute that mechanically contacts and guides portions of a moving nonwoven web in a curving manner effective to create a longitudinal fold. Other conventional folding devices include a convoluted folding belt that contacts and moves with a moving nonwoven web. The folding belt directs a portion of the nonwoven web in a twisting path that ultimately produces a longitudinal fold. However, such guides, chutes, formers and additional moving belts of conventional web folding apparatus cannot be used in an in-line process with a meltspinning apparatus to longitudinally fold an unconsolidated nonwoven web, as the mechanical contact would damage the nonwoven web in this fragile state.
In view of the deficiencies in conventional web folding apparatus discussed above, it would be desirable to provide an apparatus capable of creating a longitudinal fold in an unconsolidated nonwoven web either absent mechanical contact or, at the least, with a minimal level of mechanical contact.